One technology in the field of refrigeration involves the sorption technique. Use is here made of heat, for example in the form of waste heat from technological processes, heat from cogeneration, solar heat or geothermal heating, for cooling a medium to be cooled, in particular a fluid.
Sorption cooling systems are known in the form of absorption cooling systems and adsorption cooling systems. The absorption cooling systems belong to the group of continuously operating sorption cooling systems. Liquid substances are used as absorbents. Conventional systems primarily operate with water/lithium bromide and ammonia/water as the substance pairs.
The absorption cooling machine can often be divided into two sections. In a first section, the absorption cooling system encompasses an absorber, an ejector drift, a pump and a restrictor. This section is often referred to as the thermal compressor. Solvent circulates therein. A second section of the absorption cooling system is equipped with a liquefier, an evaporator and a restrictor. In the evaporator, the prepared cooling agent is evaporated while absorbing thermal energy from the medium to be cooled. The evaporated cooling agent then travels to the absorber, where the evaporated cooling agent is absorbed by the solvent, specifically via absorption. The absorption enthalpy (solution enthalpy) released in the process must be dissipated. Absorption of the cooling agent turns a poor solution into a rich solution. A pump brings this solution from a low absorber pressure to a high ejector drift pressure. The solvent here routinely also flows through a counter flow heat exchanger. The latter helps to increase process efficiency by reducing the heat required by the ejector drift while simultaneously lowering the heat to be dissipated from the absorber. While supplying useful heat, the cooling agent is expelled from the solvent in the ejector drift, thereby generating cooling agent vapor, which subsequently is converted into the liquid phase in the liquefier. The cooling agent recovered in this way is again relayed to the evaporator via a restrictor.
As opposed to the absorption cooling system, which uses liquid absorbents, the adsorption cooling system is characterized by using the adsorption of the evaporated cooling agent by a solid substance (adsorbent). For example, substance pairings such as water/zeolite and water/silica gel are used in conjunction with adsorption cooling systems in the field of air conditioning technology.
Refrigeration systems have undergone an enormous growth rate on the market in past years. Longer cooling chains in the food industry, higher process performances and more comfortable living and working conditions require new, efficient refrigeration systems. Electrically powered compression systems are currently dominant. Thermally driven absorption and adsorption methods are also in use. Above all against the backdrop of increasing the efficiency of energy use, to include increasing that of cogeneration systems, the latter provide a resource-saving way, in a growing market for using cold temperatures, to not additionally raise the power demand, and instead utilize the waste heat from power production directly for refrigeration purposes.